Hi, I’m writing a provider. For a resource, I wondering how to check if an optional attribute exists.
In Read function, I think it is mainly about the req.State object. Get or GetAttribute includes a lot of type-casting handling, which I don’t need, and It’s hard to tell from returned diagnostics. I’m not sure PathMatches could be a choice or not.
Hi @dreampuf 
If you have a schema that defines an optional attribute, such as the following:
func (e *exampleResource) Schema(ctx context.Context, req resource.SchemaRequest, resp *resource.SchemaResponse) {
resp.Schema = schema.Schema{
Attributes: map[string]schema.Attribute{
"configurable_attribute": schema.StringAttribute{
Optional: true,
MarkdownDescription: "Example configurable attribute",
},
},
}
}
Assuming, the associated data model looks as follows:
type exampleResourceData struct {
ConfigurableAttribute types.String `tfsdk:"configurable_attribute"`
}
Then you can check whether the optional attribute is defined in the plan in the Create method, or in the state in the Read method as follows:
func (e *exampleResource) Create(ctx context.Context, req resource.CreateRequest, resp *resource.CreateResponse) {
var data exampleResourceData
diags := req.Plan.Get(ctx, &data)
resp.Diagnostics.Append(diags...)
if resp.Diagnostics.HasError() {
return
}
if data.ConfigurableAttribute.IsNull() {
tflog.Info(ctx, "create")
}
tflog.Trace(ctx, "created a resource")
diags = resp.State.Set(ctx, &data)
resp.Diagnostics.Append(diags...)
}
func (e *exampleResource) Read(ctx context.Context, req resource.ReadRequest, resp *resource.ReadResponse) {
var data exampleResourceData
diags := req.State.Get(ctx, &data)
resp.Diagnostics.Append(diags...)
if resp.Diagnostics.HasError() {
return
}
if data.ConfigurableAttribute.IsNull() {
tflog.Info(ctx, "read")
}
diags = resp.State.Set(ctx, &data)
resp.Diagnostics.Append(diags...)
}
If the data.ConfigurableAttribute is not null, then you can obtain the string value of the attribute by calling data.ConfigurableAttribute.ValueString() or data.ConfigurableAttribute.ValueStringPointer().